Records such as conventional audio records and the newer video records are manufactured by molding a thermoplastic composition between a pair of metal discs referred to as stampers.
The stampers are manufactured by a process referred to as matrixing. The information which is desired to be molded on the final record is initially recorded on a magnetic tape. A surface relief pattern which corresponds to the recorded information is cut into a recording substrate using the magnetic tape to control the cutting tool. Conventional records, such as the audio record, are cut into a wax or laquer substrate. The new high information density record, such as the video record, are cut into hard substrates such as bright electrodeposited copper substrates. The recording substrate is then prepared for electroforming by activating the surface wax or lacquer substrates and passivating the surface of the recorded metal substrates. The recording substrate is then electroplated with a metal such as nickel to provide a master which is a negative replication of the recording substrate. The grooved surface of the master is then passivated and in turn electroplated to form a mold which is a positive replication of the recording substrate. The grooved surface of the mold is then electroplated to form a stamper which is again a negative replication of the recording substrate. The stamper is the part which is mounted in a molding press and which presses the record disc.
The quality of the records which are pressed with a given stamper is directly related to the condition of the molding surface of the stamper. If the molding surface is free from defects, the records pressed from the stampers should have excellent fidelity to the original recording. If, however, the molding surface of the stamper is mechanically damaged, such as being scratched or contaminated with foreign material such as oils or dirt, the record pressed with the stampers reflect the condition of the stampers by having relatively poor fidelity and in extreme cases the records may not even be playable.
The problem of mechanical damage and surface contamination of the molding surfaces of stampers is a long-standing problem in the record molding art. Scratching of the surface of the record stampers is one of the most prevalent causes for rejection of stampers in the manufacture of audio and video records. In addition, when the surface is contaminated by the oil or dirt or by coatings applied to the stampers or other foreign materials, it has been found that the fidelity of the audio records is also markedly reduced.
In the audio record art, it has been common practice to chromium plate the molding surface of the stampers in order to make them harder and therefore more scratch resistant and to inhibit contamination by foreign materials. These efforts at best have only had moderate success with audio record stampers as the aforementioned problems continue to persist in the audio record art.
In the manufacture of the newer type high density information records, such as the video records, wherein the recorded signal elements are much smaller than on audio record surfaces scratching and surface contamination pose considerably greater problems. The recorded signals on a high information density record are generally orders of magnitude smaller than in the signal elements on an audio record. Accordingly, scratches which would be of little concern on an audio record stamper present major problems with regard to the high information density record stampers in that often the scratches, even the microscratches, are as large or even larger than the recorded signal elements. The problem of surface contamination likewise is a more serious problem in the manufacture of high information density records as compared to the audio records. Surface contamination even such contamination as, for example, the thin film of oil from the fingerprints of the operators and the like, can impart defects to the records made with the record stampers.
The problems of mechanical damage and surface contamination are made even more complex with regard to the high information density record stampers; in that unlike the audio records stampers, they cannot be effectively chromium plated in order to improve their scratch resistance and to decrease the tendency for foreign materials to adhere to the surface of the stampers. The reason for this is that chromium plating, in order to be effective, must be applied in a relatively thick layer. The chromium plating reduces the fidelity of reproduction of information on an audio record, but it is considered to be an acceptable tradeoff for the added protection. On high information density record stampers, because of the extremely small size of the recorded signal elements, the chrome plating tends to obliterate the signal when applied in a sufficiently thick plating to offer any substantial amount of protection. For this reason, it is necessary in the manufacture of high information density records to use virgin nickel stampers which are inherently easier to scratch and are more subject to surface contamination.
It has been found that a substantial proportion of mechanical damage, and also the contamination of the surface of the stampers, occurs from the time the stamper is completed in the matrixing process until it is mounted in a press for the pressing of records. Part of the cause of the damage to the stampers is a result of the numerous handling operations the stampers are exposed to before being mounted in the molding press. In the matrixing process, it is customary to electroform in a single production run all the stampers which are anticipated to be required for the molding of a given run of records. Accordingly, as the process is being run, stampers are generated which are sent to either intermediate or longterm storage. The stampers are examined prior to being placed in storage to determine any visual defects on the stampers and an identification code is inscribed on the unrecorded center portion of the stampers for future identification of the stampers and the records pressed on the stampers.
After the inspection, the stampers are stored for future use. The molding surface was heretofore often left exposed but this has been proven to be an extremely poor practice. It has been suggested to apply a film of plastic to the surface of the stamper which can be stripped after the stamper is installed in the press. The film, however, offers at best minimal protection, and even when stripped often leaves a microresidue on the molding surface. It has also been suggested to place the stamper in an envelope similar to dust covers used for molded records or to place the stamper in a can similar to that used for the storage of motion picture films and the like. Both of these suggestions were not satisfactory as it must be removed and handled in an unprotected state when an operator is examining or working with the stamper.
When the stampers are required for the molding of the records, they are then removed from the storage area and forwarded to the molding area. In the molding area, an operator removes the stamper from its protective cover, checks the identification of the stamper, engraved in the center portion of the stamper, and then mounts the stamper onto the platens of the record molding press. In order to remove the stamper, examine it and mount it in the press, the operator is required to handle the stamper. In the course of mounting the stamper, it is almost inevitable that the operator will inadvertently contact the molding surface of the stamper leaving fingerprints on the stamper. In addition, because of the inherent presence of oils, such as hydraulic fluids and the like, in the area of the presses, it is not uncommon for substantial quantities of oily materials to contaminate the surface of the exposed stampers. It has also been found that in the course of mounting the stampers onto the press, that the stampers are highly vulnerable to being scratched. This can occur from being contacted by another stampers or by the tools used to mount the stampers which can inadvertently contact the molding surface of the stamper. Scratches are often imparted to the stamper during mounting which immediately makes the stamper unsuitable for the molding of records. There are, of course, many other situations wherein the stamper is subject to damage prior to being mounted in the stamper. Once the stamper is mounted in the press, the danger of damaging the stamper is substantially reduced in that generally the operator does not contact the molding surface of the stamper in use, and furthermore, tools are not being brought into contact with the molding surface of the stamper until it is desired to remove the stamper from the press.
Accordingly, it would be highly advantageous if an apparatus could be provided which would protect the surface of the stamper from the time it is completed in the matrixing area, until the time it is completely mounted in the press and is ready for the pressing of records.